Viking 1 was the first of a pair of complex deep space probes that were designed to reach Mars and collect evidence on the possibility (or lack thereof) for life on Mars.

Each spacecraft was composed of two primary elements, an orbiter (2,339 kilograms) and a lander (978 kilograms). The orbiter design heavily borrowed from the Mariner buses, while the lander looked superficially like a much larger version of the Surveyor lunar lander.

Prior to launch, the batteries of the first spacecraft were discharged, prompting NASA to replace the original first spacecraft with the second, which was launched as Viking 1.

After three midcourse corrections (on 27 August 1975 and 10 and 15 June 1976), the spacecraft entered orbit around Mars on 19 June 1976. Initial orbital parameters were 1,500 x 50,300 kilometers. The following day, when the orbiter began transmitting back photos of the primary landing site in the Chryse region, scientists discovered that the area was rougher than expected.

Using the new photos, scientists targeted the lander to a different site on the western slopes of Chryse Planitia. The lander separated from the orbiter, and after a complex atmospheric entry sequence, during which the probe took air samples, Viking 1 lander set down safely at 22.483° north latitude and 47.94° west longitude at 11:53:06 UT on 20 July 1976.

Once down, the spacecraft began taking high quality photographs (in three colors) of its surroundings. Instruments recorded temperatures ranging from -86°C (before dawn) to -33°C (in the afternoon). The seismometer on the lander was inoperable.

On 28 July, the lander's robot arm scooped up the first soil samples and deposited them into a special biological laboratory that included a gas chromatograph mass spectrometer. While some data could be construed as indicating the presence of life, a major test for organic compounds gave negative Results.

The lander continued to return daily (and then eventually weekly) weather reports until loss of contact on 1 February 1983. Further attempts to regain contact proved unsuccessful. The orbiter was shut down on 7 August 1980, after it ran out of attitude-control propellant.

Key Dates

20 Aug 1975: Launch (21:22 UT)

19 Jun 1976: Mars Orbit Insertion

20 Jul 1976: Mars Landing (11:53:56)

Status: Successful

Fast Facts

The Viking landers took 4,500 unprecedented images of the surrounding surface and radioed more than 3 million weather-related measurements back to Earth, while their two companion orbiters took 52,000 images of sections of the Martian globe.

Viking 1 sent back the first image from the surface of Mars (right)

Viking 1 was supposed to be Viking 2, but the launch order was switched so engineers could fix a battery problem on the first spacecraft.